Glabrous, short-lived, tap-rooted perennial; stems rather thin, wiry, flexuous, spreading, green to dark red, to c. 1 m tall. Petioles of basal lvs often very long, particularly in subaquatic plants. Lamina of lower lvs (3)-7-20-(23) × (1)-1.5-3.5 cm, oblong or ovate-oblong, ± membranous; margin often undulate and crisped; base broad-cuneate, rounded or cordate; apex acute or subacute. Stem lvs progressively smaller and extending c. ⅔ along infl. branches. Infl. many-branched, spreading and flexuous, becoming twisted. Whorls all distant; fls probably protandrous, ☿, small, dense. Pedicels slender, reddish. Perianth (0.7)-1-5 mm long; outer segments ovate, obtuse, not reflexing at fruiting; inner segments greatly enlarging at fruiting. Fruiting valves 2-2.8-(3.2) mm long, ovate, reticulate, entire, rounded at apex, generally becoming dark red, each with a large tubercle occupying ?-3/4 valve width. Nut 1.5-2 mm long, dark glossy brown or reddish brown, acutely angled.